1. Field of the Invention
Disclosed embodiments relate to a manufacturing technology using a metal pressing die, and particularly relates to a press molding die structure and a method of press molding a work in which a plate-shaped work is press molded thereby to form a product work having a three-dimensional shape.
2. Related Art
In automobile industries, there has been adopted a manufacturing technology for press molding and working materials using pressing machines such as a transfer pressing machine and a tandem pressing machine. In case of the transfer pressing machine, a 4 steps-4 dies type automatic pressing line comprising, for example, molding step, cutting step, bending step and holing (piercing) step is used. The work is in turn subjected to press working in the respective dies of the automatic pressing line.
When an operating speed is increased in these pressing machines in order to improve a production efficiency, an operating speed of each of the steps such as molding step or the like, and an elevating speed of a press upper die with respect to that of a press lower die is also increased.
However, when the operating speed of each of the steps such as molding step or the like is increased, there may be a case where the work is dragged toward the press upper die, or a part of the work is stuck to the press upper die at a time of opening the press molding dies, so that the work is randomly moved between the press upper die and the press lower die. In a serious case, there may be a case where the work flies out from the press molding dies.
Further, when the work is randomly moved and sifted, it becomes difficult to take out the work from the press molding die of a prior step and to set the work into the press molding die of a post (next) step. At any rate, the setting of the work cannot be accurately performed. Therefore, it becomes difficult to increase the operating speed of the pressing machines, so that the speed-up of the operating speed is limited to some extent.
On the other hand, in order to improve the operating speed of the pressing machines, there have been proposed a work retaining technology using a suction cup for the pressing machine which is used in the bending step of the transfer pressing machine as disclosed in a Patent Document 1.
The pressing machine disclosed in a Patent Document 1 do not direct to a press molding die used in molding step, but directs to a press molding die used in bending step. This press molding die comprises: an air cylinder accommodated in a lower die body of the press lower die; a work lifter vertically moving by the action of the air cylinder; and the suction cup provided to the work lifter.
Further, a Patent Document 2 discloses a work positioning device having a plurality of suction mechanisms each comprising: a cylinder fixed to a jig; and a suction cup in which a plate-shaped work is sucked and retained by the suction cup.